This invention relates to an electronic controlled fluid suspension system for a vehicle and especially to a controller for the suspension system for controlling roll and pitch of the vehicle body.
Various suspension systems and controllers have been proposed so far in which displacements of suspensions of a vehicle are totally controlled in order to improve riding comfort and maneuverability. In one of those prior art suspension systems, such as disclosed in an international publication WO 84/02886 (PCT/GB 84/00014), displacements of suspensions sensed by appropriate sensors are converted into displacements representing a change in the attitude of the body, i.e., vertical translational displacement, roll displacement, pitch displacement and warp displacement. Based on the displacements of various modes of body attitude change, the suspensions are controlled to stabilize the body attitude.
Such suspension control has a quick response to any attitude change caused by turning, braking and accelerating, but has a drawback in some cases. When the vehicle runs on a rough road, the controller may cause hunting by picking up high-frequency displacement changes of the suspensions corresponding to the profile of the road because of rather low responsiveness of the controller. One measure to prevent the hunting is to provide a low-pass filter between the displacement sensor at the suspension and the controller in order to eliminate the high-frequency component of the sensor signal. But this measure has still another drawback: the characteristic of the attitude control depends on the threshold frequency of the low-pass filter. Namely, the merit of the quick responsiveness of the attitude control may be sacrificed by the low-pass filter.